The invention relates to transportable apparatus and process for separating solids from used drilling mud. Liquid flow is managed in settling tanks while rotating suctions collect and deposit settled solids in a solids tank. Solids are removed by conveyor and clarified water from the tertiary settling tank is recycled to a drilling rig.
It is important during drilling of a well to control the fraction of solids in the mud used to facilitate drilling. In Southern Alberta, after surface casing, it is usual to perform drilling using water as the mud liquid for several days until gel muds are required to carry finer solids. Drilling with water is called clearwater drilling and results in fast rates of penetration while it can be used.
Solids are removed from the water so that it can be economically and environmentally recycled for re-use in the drilling process. Further, excessive amounts of solids can reduce the rate of drilling, and contaminate formations.
Prior art systems include landfarming of the used mud, the use of pits to separate solids from the mud or specialized equipment. Equipment used to separate solids from drilling mud include expensive centrifuge technology or a complicated combination of shakers, de-sand and de-silter hydroclones, settlers, floc treatment and augers.
If solids-removal equipment is to be used, because it is impractical or undesirable to use pits, then it becomes necessary to ship the equipment to the site.
Others have attempted to provide a single skid mounted apparatus for providing all the components necessary to treat used drilling mud and returned a clarified liquid for reuse in an active mud system. For example, as disclosed in U.S. Pat. No. 4,536,286 to Nugent, there is a need for a transportable waste treatment which:
Is completely mobile;
Is capable of treating high mud volumes;
Is self-contained having chemical storage, chemical pumps, sludge pumps, water pumps, laboratory, centrifuge, conveyors etc;
has weight, height and width suitable for highway travel; and
is capable of full operation shortly after delivery to the site.
Nugent discloses a skid incorporating three settling tanks and two chemical tanks for flocculation. Waste liquids containing solids enter a first settling tank and are mixed with flocculation chemicals. Solids settle to the tapered bottom of the tank for collection by a suction located at the apex of the tank bottom. Partially clarified liquid from the first settling tank overflows a weir to the next adjacent settling tank and similarly for the second to the third settling tank.
In U.S. Pat. No. 5,582,727 to Foster, a single structural skid houses four settling tanks. Each tank is equipped with a shaker and a de-silter. Used drilling mud is routed sequentially from tank to tank. Partially clarified liquid is decanted over weirs to each tank in succession. Fixed suction pumps extract settled solids from the bottom of each tank and route them to the de-silter of each additional and successive tank. Foster does not practice flocculation.
It is the applicant""s experience that one cannot use conical bottom tanks due to the resultant increase in height. An example of apparatus using conical tanks include U.S. Pat. No. 4,388,195 to von Hagel et al. which excavates a ground installation to accommodate the conical bottom.
Excess height is unacceptable due to the height restrictions for shipping on most major roadways. Typically, one would transport the separation equipment by trailer. To avoid the associated cost of integrating the apparatus with a trailer and to avoid monopolizing an expensive trailer by leaving it onsite under the separation apparatus, the separation apparatus is typically an independent skid removeably located on the trailer.
Further, once in use, the tank significantly increases in weight and is subject to settling, complicating the separation flow of liquids within the apparatus.
The prior art does not disclose a process or apparatus which is capable of minimizing the equipment, size and weight of the skid through implementation of apparatus and process for optimization of solids removal, or to distribute the weight of the overall structure to avoid imbalance and uneven settling on soft ground.
Generally the apparatus and method provide means for treating drilling mud so as to separate solids from liquid.
The apparatus is integrated into a single transportable unit. Factors contributing to the ability to provide an effective and transportable treater include novel flow path management in and between two or more settling tanks, removal of settled solids without the need for conical tank bottoms, effective solids production and weight balancing to limit uneven settling.
Some of the features include:
providing all the treatment tanks on a single structural frame or xe2x80x9cskidxe2x80x9d;
providing a system where solids are continuously removed and clarified liquid is produced;
increasing the effective residence time for the settling of particulate solids from the used mud by maximising the flow path of the mud through each settling tank;
maximizing the settling process by managing the conveyance of solids-containing liquid between settling tanks; and finally
balancing the weight of the skid through proper physical arrangement of the separate tanks based on their individual and predictable operating weights;
The apparatus and process is particularly well suited for treating the mud produced from clearwater drilling section, de-watering of drilling muds, and cleanup of rig ditch water.
In particular, the present invention collects settled solids from the flat bottom of each tank by rotating one or more radially and horizontally extending conduits about an axis so that the distal end of each conduit traverses an inscribed circular path about the periphery of the tank""s bottom, the conduits having one or more inlets facing the tank bottom and inducing suction on the conduits so as to draw settled solids into the conduits. In another aspect, the arrangement and construction of the tanks enables management of the flow of solids-containing liquids to maximize retention time of the fluids. Most preferably, this is achieved by positioning the settling tank""s liquid inlet and liquid outlets along a common wall and spacing them laterally as far apart as possible so that flow path of liquid from the inlet to the outlet of the settling tank encompasses substantially the entire settling tank. Additionally, clarified liquid from each tank""s outlet flow, via gravity, from a point adjacent one tank""s liquid surface, through inclined conduits to the inlet of the successive settling tank.
In a broad apparatus aspect then the invention comprises a skid for treating used drilling mud containing solids and liquid, the apparatus comprising two or more settling tanks, each settling tank having a flat bottom the liquid inlets and liquid outlets of each settling tank being lower than their respective liquid surfaces and being spaced laterally apart, introduced solids settling to the bottom of each tank and clarified liquid forming adjacent the liquid""s surface, the clarified liquid being produced as a clarified liquid product from the liquid outlet of the last of the successive settling tanks, there also being one or more passageways for gravity-flowing clarified liquid from the liquid outlet of one settling tank to the liquid inlet of its successive settling tank. A solids tank also forms part of the skid and accepts settled solids produced from the bottom of the settling tanks. Settling tank solids are collected using one or more conduits positioned in the bottom of each settling tank, each conduit extending radially and horizontally along the flat bottom from a rotational axis and having an inlet at its distal end which rotates with the conduit about the rotational axis so as to traverse an inscribed circular path about the periphery of the tank""s bottom. A pump creates a suction in the conduit for drawing collected solids from the tank bottom into the inlet of each conduit, the solids then being conducted through conduit means for transporting settled solids from the suction conduits to the solids tank. Finally, a conveyor has its inlet located at the bottom of the solids tank and transports solids product to an outlet located outside the skid for discharging the solids product.
Optionally, and to satisfy industry""s preference for current technology and reluctance to introduce a settling means to provide a dewatered, product, a centrifuge may be used in place of the solids tank.
Preferably, the passageways extending between a settling tank and its successive settling tank comprise one or more inclined conduits.
More preferably, the liquid inlet and outlets of each settling tank are spaced laterally along the same wall. Accordingly, the inlet of the first settling tank is preferably positioned along about the middle of an enclosing wall for directing used mud outwardly into the middle of the first settling tank and the outlets of the first settling tank are two ports are spaced far as possible from the inlet and positioned either side of the inlet so that the flow path of the used mud must be substantially outwardly towards the opposing enclosing wall and curling back to the two ports as two streams, for maximizing the length of the flow path. In combination with the inclined conduits, this permits an ideal complementary arrangement for the successive settling tank wherein the outlet of the successive settling tank is positioned at about the middle of its enclosing wall facing the first settling tank and wherein it inlet is two ports positioned as far apart as possible on either side of the outlet and along the same facing enclosing wall as the outlet so that the flow path must be two streams flowing substantially outwardly to the enclosing wall opposing the facing enclosing wall for curling back along the middle of the successive settling tank to its outlet, again for maximizing the length of the flow path.
Knowing the probable weight of the tanks during operation, the solids tank and settling tanks can be preferably pre-arranged on the skid so that the weight of the settling tanks when containing liquid and the solids tank when containing solids is balanced along the skid.
The above apparatus enables practicing of a novel method of treating used mud liquid which comprises:
providing a transportable skid having a solids tank, a first settling tank and at least one successive settling tank, each settling tank having a flat bottom;
establishing a liquid level and a diminishing liquid surface in each of the settling tanks;
spacing the liquid inlet and liquid outlets of a settling tank laterally apart for maximal retention time of the liquid;
introducing used mud to the first settling tank;
settling solids to the bottom of the first settling tank and forming an upper layer of clarified liquid;
gravity-flowing clarified liquid from each tank""s outlet to each successive settling tank;
collecting settled solids from the bottom of each tank by rotating one or more radially and horizontally extending conduits about an axis so that the distal end of each conduit traverses an inscribed circular path about the periphery of the tank""s bottom, the conduits having one or more inlets facing the tank bottom and inducing suction on the conduits so as to draw settled solids into the conduits; and
conveying settled solids to the solids tank;
withdrawing clarified liquid as a clarified liquid product from a point adjacent the liquid surface of the last of the successive settling tanks; and
conveying the solids out of the bottom of the solids tank to location located outside the skid for discharging the solids product.